The subject matter disclosed herein relates to electric generators and variable speed drive fed AC motors.
Variable speed drive (VSD) fed AC motors utilize a VSD controller to control the speed and torque of an AC motor (such as to drive a load or perform other useful work) by varying the frequency and voltage of input signals to the AC motor. Using similar physical principals, electric generators are used to convert mechanical energy into electrical energy, such as for driving a motor or other electrically powered device. Both AC motors and electric generators include stator insulation to prevent current from flowing from the rotational components of the device through the stationary components of the device. Over time, the resistance of the stator insulation in electric generators and VSD-fed AC motors degrade. The stator insulation resistance may eventually degrade to the point where the operation of the AC motor or the electric generator is severely impaired or, in extreme instances, the AC motor or the electric generator may even be rendered inoperable.
While techniques have been developed to determine the health of stator insulation of electric generators and AC motors, such techniques typically are performed with the generator or motor in an off-line state. That is, the motor cannot be operated while the needed measurements are taken, making such monitoring approaches inconvenient and inefficient.